Many natural and synthetic materials are known to be useful as lubricants, their utility in particular applications depending on factors such as their stability and viscosity under the conditions of use, their pour points, and their compatibility with any materials with which they will be used.
In refrigeration applications (e.g., home-use or industrial-use refrigerators, freezers, or air conditioners for buildings, automobiles, airplanes, and other vehicles), the need to replace chlorofluorocarbon refrigerants with a refrigerant having lesser ozone-depleting potential has made it important to find lubricants which would be suitable for use with 1,1,1,2-tetrafluoroethane (R-134a), a refrigerant that has been reported to have an ozone depletion potential of zero. Mineral oils, usually the refrigeration lubricants of choice in the past, cannot be utilized in this application because of incompatibility with R-134A.
Jolley, "New and Unique Lubricants for Use in Compressors Utilizing R-134a Refrigerant," pp. 145-152 (a paper presented at the ASHRE/Refrigeration/Compressor Engineering Conference at Purdue, July 1990), reports that preliminary tests conducted on certain esters, amides, and polyalkyleneglycols indicated that fluids of such types held the greatest promise of providing acceptable fluids for use as compressor lubricants in refrigeration applications utilizing R-134A. U.S. Pat. No. 4,992,188 (Jolley-A) indicates that the amides subjected to those preliminary tests were tertiary amides of the type obtained by reacting (1) a hydrocarbylpolyoxyalkylenealkanoic acid or (2) a hydrocarbyl mono- or dicarboxylic acid or anhydride with a secondary amine which may be a di(cyclo)alkylamine or a heterocyclic amine (such as pyrrolidines, piperidines, morpholines, and piperazines) that, except for the amino nitrogen, is hydrocarbyl in nature.
As explained in his patent, Jolley prefers his amines to be "purely" hydrocarbylamines, i.e., amines in which the hydrocarbyl groups are true hydrocarbyl groups containing no atoms other than carbon and hydrogen. However, in a less preferred embodiment of his invention, he considers it acceptable to use "substantially" hydrocarbylamines, i.e., amines in which the hydrocarbyl portion(s) contain hetero atoms or non-hydrocarbyl substituents which are of a type and number such that they do not alter the predominantly hydrocarbon nature of the group(s) as they exist in the amines and the tertiary amides produced therefrom.
Both Jolley and Jolley-A indicate that the above-described tertiary amides perform well as refrigeration lubricants when used together with R-134a and similar refrigerants, but they are uneconomical to prepare. Thus, there is still a need for amide-type lubricants which (1) like those of Jolley, would have R-134a compatibility and appropriate viscosities over the entire temperature range to which a refrigeration composition is apt to be exposed but (2) unlike Jolley's amides, could be synthesized from relatively inexpensive starting materials.
U.S. Pat. No. 4,208,293 (Zaweski) discloses amide/ester/diester-amide mixtures which are useful as additives for crankcase oils and can be obtained by reacting diethanolamine with a fatty acid that preferably contains .gtoreq.8 carbons, more preferably 8-22 carbons.
British Patent 989,009 (Produits Chimiques) teaches diester-amides of dialkanolamines which are similar to those of Zaweski in that they have the same acid residue in the amide and ester portions of the molecule but are dissimilar to Zaweski's diester-amides both in the smaller carbon content of the acid residues and in the application for which they are intended, i.e., plasticizers for vinyl resins.
U.S. Pat. No. 3,179,615 (Magne et al.) and German Auslegeschrift 1114508 (Chemische Fabrik Duren) teach other diester-amides of dialkanolamines which, like those of Produits Chimiques, have utility as plasticizers but, unlike those of Produits Chimiques and Zaweski, have different acid residues in the amide and ester portions of the molecule. The diester-amides of Magne et al. have monounsaturated and/or epoxidized alkenyl groups of 11-21 carbons as the hydrocarbyl groups in the amide portion and methyl, cyclohexyl, phenyl, or substituted phenyl groups in the ester portions. Duren's diester-amides have residues of lower mono- or dicarboxylic acids, such as formic, acetic, propionic, oxalic, malonic, maleic, or adipic acid, in the amide portion, while their ester portions have residues of higher fatty acids containing 10-24 carbons.